Research On Service Offloading Algorithm Based On Cell-Free Massive MIMO System

The fifth generation mobile communication technology(5G)puts forward higher requirements on spectrum efficiency and user experience data rate.Massive multiple-input multiple-output(Massive MIMO)is a key technology to obtain high-rate transmission and high spectral efficiency.In recent years,Cell-Free Massive MIMO technology combining distributed antenna technology and virtual Massive MIMO technology has been proposed.This architecture can achieve higher spectrum efficiency.At the same time ensure the fairness of user service quality.But compared with the traditional MIMO technology,this architecture will bring higher backhaul link load and higher system complexity due to the characteristics that all antennas serve all users at the same time,one of the main research contents of this paper is the scalable architecture to reduce the backhaul link load of CF Massive MIMO system.In addition,since this architecture does not have the concept of cells in traditional MIMO,there is no complete service offloading solution under this system,so the service offloading method under this system is also one of the issues that need to be studied in the current Cell-Free Massive MIMO system.This paper first analyzes the basic principles and key technologies of Cell-Free Massive MIMO,including its uplink and downlink training process and data transmission process.Then,the spectrum efficiency of the Cell-Free Massive MIMO system and the traditional cell system are analyzed and compared.Based on the above theoretical analysis and model construction,combined with the research focus of User-Centric(UC)under this system,this paper then studies the simplified user-centric architecture of Cell-Free Massive MIMO system.This architecture aims to reduce the system backhaul link load.First,three simplified algorithms for this system are introduced: part local processing method,all local processing method and small cell method.Then a new,user-centric simplified algorithm,the user-side constraint method,is proposed.Compared with the existing algorithms,this algorithm can greatly reduce the load of the backhaul link on the basis of ensuring user spectral efficiency and user fairness.Finally,this paper studies the service offloading algorithm based on the user-side constraint method.The rules for service offloading in the traditional cell system are clear.There is no mature service offloading algorithm research in Cell-Free Massive MIMO systems.Based on this system architecture and combining large-scale fading tracking based on Bayesian estimation,this paper designs a service offloading algorithm.By tracking large-scale fading,the channel state information at the next moment can be obtained in advance,thus providing a theoretical basis for offloading the service to the corresponding access point at the next moment.Theoretical analysis and simulation experiment results show that this algorithm can effectively reduce the backhaul link load in the system,and at the same time perform service offload in advance through large-scale fading tracking,which can reduce the total delay of service offload and increase the amount of service offload.The conclusion summarizes the research results of the full text,and discusses some unsolved problems and future research directions of service offloading in Cell-Free Massive MIMO systems.